1. Field of the Invention
The present invention relates to a Phase Locked Loop (PLL) circuit, and more particularly to a PLL circuit containing therein dead time.
2. Description of the Related Art
The evolution of signal processing from analog to digital results in that complicated processing which had been difficult to carry out is realized in related art, and problems in process variation are fundamentally dissolved.
On the other hand, however, the signal processing based on the digital implementation has a tendency to increase delay due to the digital processing.
Although this increase is not a problem so much when a signal flows in one direction, in loop processing in the PLL or the like, a system is easy to become instable.
In a control theory, this delay is referred to as “dead time,” and is distinguished from “delay time” which occurs in a low-pass filter or the like.
The PLL containing the dead time in the loop appears in various kinds of actual applications such as storage, a communication or a broadcasting.
As well known in the control theory, this dead time causes the loop characteristics to be unstable, and deteriorates stabilization characteristics.
A Smith method has been known from time immemorial as a method of compensating for the dead time in the loop. The Smith method is disclosed in U.S. Pat. No. 3,141,982, Filed on Jan. 6, 1960, Patented on Jul. 21, 1964, “CONTROL SYSTEM FOR USE IN CONTROL OF LOOPS WITH DEAD TIME” by Otto J. M. Smith.